Hybrid power system

Abstract

A hybrid power system for an aircraft comprises a gas turbine connected to a generator for generating electrical power; an electrical storage device configured to output electrical power; a propulsor; a motor operable to drive the propulsor using electrical power from either or both of the generator and the electrical storage device; and a controller. The controller, to meet propulsor power demand, is configured to control an amount of electrical power generated by the generator, and an amount of electrical power outputted by the electrical storage device. In a first control mode coinciding with an increase in the propulsor power demand sufficient to cause a transient excursion of the operating point of a compressor of the gas turbine from a steady state working line, the controller is further configured to temporarily increase the amount of electrical power outputted by the electrical storage device such that the transient excursion is reduced.

1 . A hybrid power system for an aircraft comprising:
 a gas turbine connected to a generator for generating electrical power;   an electrical storage device configured to output electrical power;   
       a propulsor;
 a motor operable to drive the propulsor using electrical power from either or both of the generator and the electrical storage device; and 
 a controller which, to meet a propulsor power demand, is configured to control (i) an amount of electrical power generated by the generator, and (ii) an amount of electrical power outputted by the electrical storage device; 
 wherein, in a first control mode coinciding with an increase in the propulsor power demand sufficient to cause a transient excursion of the operating point of a compressor of the gas turbine from a steady state working line, the controller is further configured to temporarily increase the amount of electrical power outputted by the electrical storage device such that the transient excursion is reduced. 
 
     
     
         2 . A hybrid power system for an aircraft according to  claim 1 , wherein:
 the electrical storage device is further configured to receive electrical power from the generator; and the controller, to meet a propulsor power demand, is further configured to control (i) the amount of electrical power generated by the first generator, and (ii) an amount of electrical power received by the electrical storage device from the generator;   wherein in a second control mode coinciding with a decrease in the propulsor power demand sufficient to cause a transient excursion of the operating point of the compressor of the gas turbine from a steady state working line, the controller is further configured to temporarily increase the amount of electrical power received by the electrical storage device such that the transient excursion is reduced.   
     
     
         3 . The hybrid power system of  claim 2 , wherein the controller is configured to:
 monitor a state of charge of the electrical storage system; and   when the state of charge is lower than a target state of charge, increase the state of charge by increasing the power output of the gas turbine in excess of that required by the propulsor power demand such that the electrical storage system receives electrical power from the generator, and
 when the state of charge is higher than the target state of charge, decrease the state of charge by decreasing the power output of the generator to be less than that required by the propulsor power demand such that the electrical storage system outputs electrical power to the motor. 
   
     
     
         4 . The hybrid power system of  claim 2 , wherein:
 the controller is configured in the second control mode to detect an increase in the rate of decrease of the current generated by the generator caused by a decrease in the propulsor power demand and, in response increase the amount of electrical power received by the electrical storage device to constrain the rate of decrease in the current generated by the generator to within a predetermined limit.   
     
     
         5 . The hybrid power system of  claim 2 , wherein:
 the controller is configured in the second control mode to use the model to calculate a target current to be received by the electrical storage device in response to a decrease in the power consumption of the motor.   
     
     
         6 . The hybrid power system of  claim 1 , wherein:
 the generator is configured to generate power at a constant DC voltage such that the current generated by the generator varies when the propulsor power demand varies; and
 the controller is configured in the first control mode to detect an increase in the rate of increase of the current generated by the generator caused by an increase in the propulsor power demand, and in response increase the amount of current output by the electrical storage device to constrain the rate of increase in the current generated by the generator to within a predetermined limit. 
   
     
     
         7 . The hybrid power system of  claim 6 , wherein:
 the controller is configured in the second control mode to detect an increase in the rate of decrease of the current generated by the generator caused by a decrease in the propulsor power demand and, in response increase the amount of electrical power received by the electrical storage device to constrain the rate of decrease in the current generated by the generator to within a predetermined limit.   
     
     
         8 . The hybrid power system of  claim 1 , wherein:
 the generator is configured to provide electrical power to the motor at a first DC voltage and first DC current,   the electrical storage device is configured to provide electrical power to the motor at a second DC voltage and a second DC current, and   the controller is configured to control the first and second DC voltages using DC voltage droop control by setting a droop percentage or droop virtual resistance and setting a transient response of the controller such that the second DC current increases at a rate faster than the first DC current.   
     
     
         9 . The hybrid power system of  claim 1 , wherein:
 the generator and the electrical storage device are configured to generate electrical power at a constant DC voltage, and   the controller includes a model of desired propulsor responses, and is configured to monitor the power consumption of the motor, and in the first control mode to use the model to calculate a target current to be output by the electrical storage device in response to an increase in the power consumption of the motor.   
     
     
         10 . The hybrid power system of  claim 9 , wherein:
 the controller is configured in the second control mode to use the model to calculate a target current to be received by the electrical storage device in response to a decrease in the power consumption of the motor.   
     
     
         11 . The hybrid power system of  claim 1 , wherein the controller is configured to:
 calculate a power excess amount which is the difference between the propulsor power demand and the propulsor power achieved by operating the gas turbine operating at a predetermined operating point; and
 when the power excess amount is positive, increase the amount of electrical power output by the electrical storage device, and when the power excess amount is negative, increase the amount of power received by the electrical storage device. 
   
     
     
         12 . An aircraft fitted with one or more of the hybrid power systems of  claim 1 . 
     
     
         13 . A hybrid power system for an aircraft comprising:
 a propulsor;   a gas turbine for driving the propulsor via a purely mechanical drive train that extends from the gas turbine to the propulsor;   
       an electrical storage device configured to output electrical power;
 a motor connecting to the drive train and operable to drive the propulsor using electrical power from the electrical storage device; 
 a controller which, to meet a propulsor power demand, is configured to control (i) an amount of torque transmitted to the propulsor from the gas turbine, and (ii) an amount of electrical power outputted by the electrical storage device; 
 wherein, in a first control mode coinciding with an increase in the propulsor power demand sufficient to cause a transient excursion of the operating point of a compressor of the gas turbine from a steady state working line, the controller is further configured to temporarily increase the amount of electrical power outputted by the electrical storage device such that the transient excursion is reduced. 
 
     
     
         14 . A hybrid power system for an aircraft according to  claim 13 , wherein:
 the electrical storage device is further configured to receive electrical power;
 the motor is operable as a generator to extract power from the gas turbine and provide electrical power to the electrical storage device; and 
 the controller, to meet a propulsor power demand, is further configured to control (i) the amount of torque transmitted to the propulsor from the gas turbine, and (ii) an amount of electrical power received by the electrical storage device from the motor operating as a generator; 
 wherein in a second control mode coinciding with a decrease in the propulsor power demand sufficient to cause a transient excursion of the operating point of the compressor of the gas turbine from a steady state working line, the controller is further configured to temporarily increase the amount of electrical power received by the electrical storage device such that the transient excursion is reduced. 
   
     
     
         15 . The hybrid power system of  claim 13 , wherein the controller is configured to:
 monitor a state of charge of the electrical storage system; and
 when the state of charge is lower than a target state of charge, increase the state of charge by increasing the power output of the gas turbine in excess of that required by the propulsor power demand such that the electrical storage system receives electrical power from the motor operating as a generator, and 
 when the state of charge is higher than the target state of charge, decrease the state of charge by decreasing the power output of the gas turbine to be less than that required by the propulsor power demand such that the electrical storage system outputs electrical power to the motor.